The strengthening of yarn spun from anisotropic-melt forming polyesters is taught in Luise U.S. Pat. No. 4,183,895. The Patenteeacknowledges that heat treatment may cause fusion between the filaments which can make it impractical to rewind the yarn. It is suggested in said patent that useful results have been obtained if the filaments are precoated with a thin layer of an inert substance, for example, talc, graphite or alumina. Further improvements are, however, desired to prevent sticking of filaments to each other during heat treatment. The use of anisotropic-melt polyester fiber has been suggested for composite reinforcement. The need to promote the adhesion of such fiber to matrices in composites has also been recognized. This invention provides improvements in these areas.